Reference to an array representing a one dimensional luminance histogram. This key is only present if image_info is invoked as image_info($file, L1D_Histogram=>1). The range is from 0 to 255, however auto-vivification is used so a null field is also 0, and the array may not actually contain 255 fields.

$Image::Info::XPM::RGBLIB is set to /usr/X11R6/lib/X11/rgb.txt or an equivalent path (see the _get_rgb_txt function for the complete list) by default, this is used to resolve textual color names to their RGB counterparts.